The present invention relates to a gimbal for supporting a hydrodynamic air bearing slider over a rotating magnetic medium. More specifically, this invention relates to a self-aligning gimbal that may be secured to the slider without adhesive.
Within a disk drive, a load beam supports a hydrodynamic air bearing slider close to a rotating magnetic disk. The load beam supplies a downward force that counteracts the hydrodynamic lifting force developed by the slider's air bearing. The slider carries a magnetic transducer for communication with individual bit positions on the rotating magnetic disk.
A gimbal is positioned between the load beam and the slider. The gimbal resiliently supports the slider and allows it to pitch and roll while it follows the topography of the rotating disk. As such, the gimbal is a critical element in a magnetic disk drive unit.
Typically, the gimbal is welded to the load beam and is connected to the slider by an adhesive. For example, with both ring-type and beam-type gimbals, the slider is adhesively bonded to a central tongue, or pad, which is supported by resilient beams. Adhesive bonds present several concerns to a gimbal designer.
First, it is generally known that the strength of an adhesive bond is proportional to the size of the bonded area. With the noted gimbal "types", a strong bond between the gimbal and the slider requires a large tongue area. However, enlarging the tongue area increases separation between the resilient beams which excessively increases the pitch and roll stiffness of the gimbal. Thus, the designer is faced with a tradeoff between bond strength and gimbal performance, both of which strongly affect reliability of the disk drive.
Second, adhesive bonds are susceptible to adhesive "bridging". Bridging occurs when the adhesive is squeezed out from an interface between the slider and the tongue and makes a connection to one or more of the resilient beams. This connection prevents the gimbal from performing properly.
Third, adhesive bonds are susceptible to adhesive "wedging". Wedging occurs when the adhesive creates a thin bond near the center of the tongue, and a much thicker bond near the ends of the tongue. This creates a stress condition where the tongue is compressing the adhesive at the ends of the tongue and pulling the adhesive near the center of the tongue. The presence of a pulling load creates a tensile stress that can approach the tensile strength of the adhesive. When the tensile stress exceeds the tensile strength of the adhesive, the bond will break allowing the slider to detach itself from the gimbal.
A fourth concern is the mismatch of the coefficient of thermal expansion ratios of the gimbal material and the slider material. A change in temperature will cause the materials to expand at different rates, which strains the slider and causes the slider to buckle and deform the hydrodynamic air bearing surface.
Fifth, the thin layer of adhesive between the gimbal and the slider creates an electrical insulator. During operation, turbulent air flow around the slider causes a buildup of electrical charge on the slider. This charge must be "bled off" to prevent a discharge across the very small gap between the transducer and the disk. Such a discharge could affect the magnetic recordings on the disk.
A final concern is achieving a desired alignment between the gimbal and the slider. Most gimbals include a load bearing dimple about which the slider can pitch and roll while following the topography of the rotating disk. To achieve a desired fly height, fly pitch and fly roll of the slider, the load bearing dimple must be located with great accuracy with respect to the slider. In a most common method of alignment, tooling alignment pins are used to match up load beam reference holes with gimbal reference holes and gimbal reference holes with slider reference features. Several tolerances can accumulate to reduce alignment accuracy. The tolerances include: load beam reference holes to tooling alignment pins; load beam reference holes to gimbal reference holes; gimbal reference holes to gimbal dimple; tooling alignment pins to slider reference features; and location of the air bearing surface on the slider.
To reduce or eliminate the above concerns, a gimbal incorporating self-attachment features that do not require the use of adhesives is desired. Wisely U.S. Pat. No. 4,141,050 and Meier et al U.S. Pat. 4,449,155 discloses gimbals with similar self-attachment features. These gimbals each include "fingers" that are wedged into a recessed channel of the slider and apply an outward force against the interior walls of the recessed channel to secure the slider to the gimbal. While the above-mentioned patents do reduce or eliminate many of the concerns associated with adhesive bonds, they do not significantly reduce the accumulation of tolerances during alignment. Further, the wedged fingers have a tendency to cause the slider to buckle and deform the hydrodynamic air bearing surface.